In recent years, a rectangular wire has been used for electric equipment such as an automotive motor and the like. The rectangular wire is a wire in which a coating section is formed around a rectangular conductor having a rectangular cross-section. As the rectangular wire has a high space factor compared to a wire having a circular cross-section, miniaturization of the equipment and high output can be realized. Patent Document 1 and 2 disclose the technology related to a rectangular wire.
Patent Document 1 discloses a method for manufacturing a rectangular wire. Specifically, a method for forming a coating section by passing through a rectangular conductor inside a tank filled with an insulating varnish and then heated to harden the insulating varnish is disclosed in Patent Document 1. Furthermore, a method for forming a coating section by spraying an insulating varnish and then heated to harden the insulating varnish is disclosed in Patent Document 1.
Patent Document 2 discloses a method for forming a uniform coating section for the purpose of improving the space factor and the like. Specifically, a coating die for forming a coating section includes 4 die parts disposed along the 4 sides of a rectangular conductor. Each of the die parts applies insulating varnish to the rectangular conductor by spraying the insulating varnish from a groove formed on the die part. With respect to each die part, a groove formed at an opposite plane of the corner region (the region on which dog bone is formed) is small. Because of this configuration, applying too much insulating varnish on the corner region of the rectangular conductor can be prevented, and the coating section can be formed uniformly.